1. Field of the Invention
The present invention relates to an endoscopic image pickup unit which can change optical characteristics of an objective optical system disposed in an endoscope.
2. Description of the Related Art
As is well known, electronic endoscopes are widely used to carry out observations, treatments, and the like in the body (body cavity) of a living organism as well as to carry out inspections, repairs, and the like in industrial plant facilities. Some recent electronic endoscopes use an image pickup unit which can change focal length for a focusing function or zooming function by moving an observation optical system toward a photographic optical axis, where the focusing function is used for focus adjustment and the zooming function is used to switch between a wide zoom and tele zoom.
In relation to an image pickup unit installed in such an endoscope, a technique for changing optical characteristics for a zooming function and the like by moving a movable lens frame forward and backward is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2003-230532.
Japanese Patent Application Laid-Open Publication No. 2003-230532 discloses an endoscopic image pickup unit equipped with an objective optical system which has a front-group lens frame, a rear-group lens frame, and a movable lens frame which moves forward and backward along the photographic optical axis in the rear-group lens frame. The conventional image pickup unit is fixed to a distal end body when a fixing screw screwed into the distal end body presses an outer peripheral portion of the objective optical system in a circumferential direction.
Also, for example, Japanese Patent Application Laid-Open Publication No. 2007-229155 discloses an endoscope equipped with an actuator unit which controls forward and backward movements of a movable lens frame using a spring and shape-memory alloy wire.